The present invention relates to technology effective when applied to a semiconductor integrated circuit for communication incorporating a voltage-controlled oscillator circuit, particularly an oscillator circuit using a quartz oscillator, and a radio communication apparatus using the semiconductor integrated circuit for communication. The technology is effectively applicable, for example, in a high-frequency semiconductor integrated circuit incorporating an oscillator circuit which generates a reference clock signal for use in processing transmit and received signals, by being used in a case where oscillation frequency information as a digital signal is given from a baseband circuit.
In the inventions described in the patent documents 1 to 4, a semiconductor integrated circuit incorporating a voltage-controlled oscillator circuit (VCO) is provided with a D/A converter enabling oscillation frequency control by means of a digital signal.
In the invention described in the patent document 1, a first counter for counting oscillator signals of a voltage-controlled oscillator circuit (VCO), a second counter for counting reference frequency signals, an AND circuit for taking a logical AND of outputs of the two counters, a third counter for counting outputs of the AND circuit, a register for holding an output of the third counter, and a D/A converter circuit for converting a digital value held in the register into an analog signal are provided, and the output of the D/A converter circuit is used to control the oscillation frequency of the VCO, enabling a center frequency to be automatically adjusted.
The invention described in the patent document 2 relates to a PLL frequency synthesizer using a multi-modulus prescaler capable of reducing noise effect on a high-frequency RF circuit.
In the invention described in the patent document 3, a pulse arithmetic circuit which computes the number of times a 1-bit D/A converter is to be driven based on the difference between the latest digital temperature-compensated data that corresponds to a temperature sensor output obtained from a ROM and the immediately preceding digital temperature-compensated data, the 1-bit D/A converter to be controlled based on the output of the pulse arithmetic circuit, and an analog accumulator which updates its output by sequentially adding the output of the 1-bit D/A converter to its current output are provided. The oscillation frequency of the digital temperature-compensated oscillator (VCXO) is prevented from changing sharply with temperature variation, and phase modulation errors of a communication apparatus using the VCXO can be reduced.
According to the invention described in the patent document 4, in a frequency hopping radio communication apparatus using spectrum diffusion technology, an antenna terminal is disposed in a central part of one end portion of the package, a transmit data input terminal and a received data output terminal are disposed in two side portions of the other end portion of the package, and a PLL frequency synthesizer circuit is disposed in an approximately central portion of the package. In this arrangement, a transmission circuit and a reception circuit are discretely disposed on two side portions of the package with the PLL frequency synthesizer circuit disposed between the two circuits so as to prevent data omission and error rate deterioration due to mutual interference between signals.    Patent document 1: Japanese Unexamined Patent Publication No. Hei 8 (1996)-307252    Patent document 2: Japanese Unexamined Patent Publication No. 2003-124808    Patent document 3: Japanese Unexamined Patent Publication No. 2003-152449    Patent document 4: Japanese Unexamined Patent Publication No. 2001-186048